The inner surface of a pneumatic tire is typically comprised of an elastomeric composition designed to prevent or retard the permeation of air and moisture into the carcass from the tire's inner air chamber. It is often referred to as an innerliner. Innerliners have also been used for many years in most tubeless pneumatic vehicle tires to retard or prevent the escape of air used to inflate the tire, thereby maintaining tire pressure for extended periods and eliminating the need to frequently pump air into the tire.
Rubbers, such as butyl and halobutyl rubber, which are relatively impermeable to air are often used as a major proportion of innerliners. For instance, U.S. Pat. No. 2,676,636 discloses the use of butyl rubber as a highly air-impermeable innerliner for tires. Halobutyl rubbers are frequently employed as innerliners because they offer both excellent gas barrier properties and low temperature flexural properties.
The innerliner is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and their methods of preparation are well known to those having skill in such art.
Halobutyl rubber is generally the most expensive rubber used in a tire. Given the competitive tire market and the continued need to lower the cost of manufacturing tires without sacrificing properties, there exists a need to eliminate or substantially decrease the cost of innerliners. In response to this need over the years a number of alternatives to halobutyl rubber innerliners have been developed. For example, U.S. Pat. No. 4,549,593 discloses a innerliner composition which is comprised of a blend of natural rubber and halogenated butyl rubber. British Patent 2,198,138 indicates that the need for an innerliner can be eliminated by utilizing a blend of styrene-butadiene rubber and a rubber which promotes adhesiveness, such as natural rubber, as the tire carcass.
U.S. Pat. No. 5,091,467 discloses an elastomeric barrier material which can be utilized as the innerliner of a tire. The barrier material disclosed therein is a melt blend of syndiotactic-1,2-polybutadiene, a terpolymer of ethylene, vinyl acetate, and vinyl alcohol, and a compatibilizing agent.
U.S. Pat. No. 5,178,702 discloses a pneumatic rubber tire having an integral innerliner comprising a top layer and rubber laminate having at least three layers wherein
(a) at least two of said three layers are barrier layers each comprised of a sulfur-cured rubber composition containing, based on 100 parts by weight of rubber,
100 parts by weight of acrylonitrile/diene copolymer having an acrylonitrile content ranging from 30 to 45 percent and from 25 to 150 parts by weight of a platy filler selected from the group consisting of talc, mica and mixtures thereof; and
(b) the thickness of each barrier layer containing 100 parts by weight of acrylonitrile/diene copolymer ranges from 25 microns to 380 microns; and
(c) interdispersed between the two barrier layers of sulfur-cured rubber containing 100 parts of acrylonitrile/diene copolymer is at least one nonbarrier layer of a sulfur-cured rubber selected from the group consisting of natural rubber, halogenated butyl rubber, styrene/butadiene rubber, cis-1,4-polybutadiene, cis-1,4-polyisoprene, styrene/isoprene/butadiene rubber, butyl rubber and mixtures thereof.